The present invention relates generally to an improved thermally conductive and electrically insulative laminate for use as a mounting pad and electrical chassis barrier in combination with solid-state electronic devices, particularly for mounting such devices with an electrically insulative layer being interposed between the thermally conductive base of the solid-state device and the chassis or other ultimate heat sink and wherein the pad is provided with tubular projections for insulatively protecting the shanks of the mounting screws or bolts from contact with the substrate including any electrical conductors disposed thereon. The properties required are that the laminates be both thermally conductive, electrically insulative, and conformable to the devices being received or mounted thereon, a combination of properties not readily found in nature.
Mounting pads for solid-state devices have been known in the past, with examples of such devices being disclosed and claimed in copending application Ser. No. 584,897, filed Feb. 29, 1984, and entitled "MOUNTING PAD FOR SOLID-STATE DEVICES". The present invention, while utilizing certain features of the device disclosed in copending application Ser. No. 584,897, is provided with the additional feature of self-locking tubular projections which extend along an axis normal to the plane of the mounting pad.
In the assembly of electronic systems, it is frequently desirable, as one operation, to initially set the mounting pad in place on a circuit board or other mounting substrate. In certain applications the mounting pad may be set in place, with the next operation including the actual positioning of the solid-state device on the pad. However, in certain assembly operations and systems, it may become desirable to move, rotate, invert, or otherwise shift the positioning of the substrate in such a way that it becomes desirable for the mounting pad to be at least temporarily held or affixed to the substrate. In accordance with the present invention, a system is provided which includes providing tubular projections for the mounting pad which are designed to extend through the thickness of the substrate, and which are provided with retention burrs for holding the mounting pad in place prior to receiving the solid-state device thereon.
It is desirable that the mounting pad be thermally conductive and electrically insulative.
Materials, including elements, compounds, and compositions of matter rarely possess the combined properties of being both thermally conductive and electrically insulative. Since the number of materials possessing such a combination of properties is relatively limited, one must seek compromises in other physical and electrical properties in order to find a useful material. Also, one technique for decreasing the thermal impedance in an electrically insulative material is to provide a material with an extremely thin cross-sectional thickness. However, as the cross-sectional thickness decreases, the risk of rupture, cracking, or fracture of the material increases, thereby increasing the risk for electrical failures. Also, in the present arrangement, a flexible tubular projection is employed, along with flexible retention burrs, so as to provide for suitable electrical insulation and mechanical durability to achieve appropriate mounting of the solid-state device on the mounting pad.
Further desirable properties or characteristics include toughness, and mechanical durability, these properties rendering the barrier member resistent to cutting, ripping, cracking, or puncturing during subsequent assembly operations. In addition, it is desirable that the barrier member per se be reasonably pliable so as to increase the area of surface contact in order to maximize the heat transfer, with the tubular projections and retention burrs being, of course, reasonably resilient, pliable, and mechanically tough. The mechanical properties are desirable in order to provide an electrical chassis barrier member which is sufficiently tough and durable to withstand the forces of over-torqued mounting screws or bolts, and furthermore reduce the occurrences of burr cut-through or cracking, which are frequent occurrences in production operations.
With respect to other physical-thermal properties which are desirable for use in combination with high power type solid-state devices, and in addition to being thermally conductive, it is desirable that the material possess an appropriate high temperature capability.
In co-pending application Ser. No. 584,897, filed Feb. 29, 1984, it is suggested that a laminate utilizing polyimide (amide) film be employed for use in combination with power type semiconductor devices. Such devices have, of course, been found to be highly useful for device mounting applications. The devices of the present invention may also employ a laminate structure for the mounting pad portion of the device, with the tubular projections and retention burrs being fabricated from silicone rubber or other desired moldable substrate material.